Prediction of residual stress-induced cracking by finite element analysis

Abstract

With the development of new ceramic materials, including those for structural applications, there is an increasing demand to join ceramic components to metal structures. The main problem in joining ceramics to metals is the thermal expansion mismatch between the ceramic and the metal. Typically, metals have higher coefficients of thermal expansion (CTEs) than ceramics. The difference in the CTEs can lead to very high stress at the brazed region during cooling from the brazing temperature to room temperature. The high stress sometimes results in cracking of either the ceramic or the interface. The residual stresses may also degrade the mechanical strength of the brazed system. Therefore, the thermal stress problems should be overcome to obtain a reliable joint between the ceramic and the metal. An alumina-to-carbon steel joint was fabricated with a direct brazing technique. The residual stress distribution in alumina near interface is determined by finite element method (FEM) analysis and the analyzed results were verified by X-ray diffraction (XRD) measurements. In order to observe the predicted cracks in detail, the joining samples were sectioned, polished and characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS).